Folding wing aircraft have found particular utility for service aboard aircraft carriers. Such aircraft typically have inboard wing sections which are pivotally connected to outboard wing sections. The outboard wing sections are thus foldable with respect to the inboard wing sections, reducing the surface area required to stow the aircraft aboard a vessel. The wing fold axis is typically aligned with the fuselage of the aircraft and transverse to the axis of the wing.
Airflow control surfaces are generally present on the foldable wings. For example, the wings have flight control surfaces, such as ailerons, and high lift control surfaces, such as leading edge slats and trailing edge flaps. These control surfaces traverse the wing fold axis so that the control surfaces are divided into inboard and outboard control surface sections. Mechanisms are provided to drive these surfaces across the wing fold axis.
Among modern folding wing aircraft, leading edge slats are typically connected to the wing by tracks which guide the slats and flaps along controlled paths. The slats (hereinafter referred to as control surfaces) are deiven by ball screw actuators or other devices, such as rotary geared power hinges, located at various points along the wing. The ball screw actuators require a rotary input to move the control surfaces. Thus, torque tubes are provided in the interior of the wing to transmit torque from a fuselage-mounted gear box through the inboard wing section and across the wing fold axis to the outboard wing section.
The torque tubes are typically transverse to and displaced from the wing fold axis. Universal joints are often provided wherever a torque tube intersects a wing rib so that flexure of the wing does not bind the drive system. At the wing fold axis, a particular geometric problem is encountered because the drive axis, defined by the torque tubes, is both displaced from, and often an angle of more than 90.degree. relative to, the wing fold axis. Furthermore, the angle with which the outboard wing section is pivotable with respect to the inboard wing section is often more than 90.degree.. Thus, the outboard torque tube becomes displaced from the inboard torque tube through a compound motion.
As stated above, mechanisms are presently employed to transmit torque across the wing fold axis from the inboard wing section to the outboard section. One mechanism utilizes a wing fold gearbox having a dog clutch. The dog clutch has a plurality of interlocking fingers which engage one another when the wing is unfolded (i.e., wings spread). When the wing is folded, the fingers disengage one another. Thus, the inboard torque tubes are disengaged from the outboard torque tubes. While this system permits torque to be transmitted across the wing fold axis when the wings are spread, the control surfaces cannot be operated when the wings are folded. This is particularly disadvantageous when maintenance is required on the control surface systems. Furthermore, it is possible for a mechanic to manually engage the fingers of the dog clutch on the outboard wing section when the wings are folded with a wrench or other implement, possibly placing the inboard and outboard control surfaces out of synchronization when the wings are unfolded.
Therefore, a need exits for a system which can transmit torque across a wing fold axis on folding wing aircraft which is highly reliable, light in weight and which can transmit torque across the wing fold axis while the wings are folded or being folded.